Fuel Cell Vehicle Simulation – Part 1: Benchmarking Available Fuel Cell Vehicle Simulation Tools

Fuel cell vehicle simulation is one method for systematic and fast investigation of the different vehicle options (fuel choice, hybridization, reformer technologies). However, a sufficient modeling program, capable of modeling the different design options, is not available today. Modern simulation programs should be capable of serving as tools for analysis as well as development. Shortfalls of the existing programs, initially developed for internal combustion engine hybrid vehicles, are: (i)Insufficient modeling of transient characteristics; (ii) Insufficient modeling of the fuel cells system; (iii) Insufficient modeling of advanced hybrid systems; (iv) Employment of a non‐causal (backwards looking) structure; (v) Significant shortcomings in the area of controls. In the area of analysis, a modeling tool for fuel cell vehicles needs to address the transient dynamic interaction between the electric drive train and the fuel cell system. Especially for vehicles with slow responding on‐board fuel processor, this interaction is very different from the interaction between a battery (as power source) and an electric drive train in an electric vehicle design. Non‐transient modeling leads to inaccurate predictions of vehicle performance and fuel consumption. When applied in the area of development, the existing programs do not support the employment of newer techniques, such as rapid prototyping. This is because the program structure merges control algorithms and component models, or different control algorithms (from different components) are lumped together in one single control block and not assigned to individual components as they are in real vehicles. In both cases, the transfer of control algorithms from the model into existing hardware is not possible. This paper is the first part of a three part series and benchmarks the “state of the art” of existing programs. The second paper introduces a new simulation program, which tries to overcome existing barriers. Specifically it explicitly recognizes the dynamic interaction between fuel cell system, drive train and optional additional energy storage.     

Strategies for Dimensioning Two‐Wheeled Fuel Cell Hybrid Electric Vehicles Using Numerical Analysis Software

Owing to the limitation of fossil fuels and high consumption and pollution for transportation, the vehicle industry is looking for other sources of energy. A fuel cell hybrid electric vehicle (FCHEV) could be a suitable solution considering the state of the art of main components. This paper presents the simulation of powertrains for FCHEVs in order to dimension the fuel cell (FC) as primary source of energy and to investigate the power flows during both motoring and recuperative braking. For this purpose a Matlab/Simulink^® model has been built up which can be used for a wide range of applications. The results of simulation show which is the best powertrain configuration for two‐wheeled vehicles in three different cases: a bike in which the traction force is provided by both electric motor and the pedaling of the cyclist, a bike in which the traction force is provided only by an electric motor without pedaling and a motorcycle for 2 passengers. Specifically, the consumption, the state of charge (SOC) of battery and the amount of energy generated by each source of energy have been monitored. The model validation was done by comparison between the obtained results and scientific articles in the literature.     

High Temperature Micro‐Fan for Solid Oxide Fuel Cell Applications

The possibility of using a μ‐fan in tubular solid oxide fuel cells module (SOFC‐M) is shown. The μ‐fan is placed instead of the ejector and fulfills its role. The main advantages of this solution are: lower power demanded by the fuel compressor (blower), more stable working characteristics, and the possibility of more accurate control of the recycled part of the anode gas during part load operation. A comparison of two SOFC‐Ms, with and without the ejector, is also shown and commented.     

Modelling and Performance Evaluation of Solid Oxide Fuel Cell for Building Integrated Co‐ and Polygeneration

Models of fuel cell based combined heat and power systems, used in building energy performance simulation codes, are often based on simple black or grey box models. To model a specific device, input data from experiments are often required for calibration. This paper presents an approach for the theoretical derivation of such data. A generic solid oxide fuel cell (SOFC) system model is described that is specifically developed for the evaluation of building integrated co‐ or polygeneration. First, a detailed computational cell model is developed for a planar SOFC and validated with available numerical and experimental data for intermediate and high temperature SOFCs with internal reforming (IT‐DIR and HT‐DIR). Results of sensitivity analyses on fuel utilisation and air excess ratio are given. Second, the cell model is extended to the stack model, considering stack pressure losses and the radiative heat transfer effect from the stack to the air flow. Third, two system designs based on the IT‐DIR and HT‐DIR SOFCs are modelled. Electric and CHP efficiencies are given for the two systems, as well as performance characteristics, to be used in simulations of building integrated co‐ and polygeneration systems.     

Hybrid Polyaryletherketone Membranes for Fuel Cell Applications

Hybrid membranes incorporating an inorganic and organic component are receiving much attention as promising solid electrolytes for fuel cells. Recent developments in the approaches to the preparation of hybrid membranes are described. The preparation and characterisation, including their performance in a hydrogen – oxygen fuel cell, of two examples of hybrid systems based on sulfonated polyaryletherketone are described. The examples are chosen to illustrate the formation in situ of inorganic particles, either in a pre-formed membrane, or in a polymer solution. sPEEK-modified silica and sPEEK-zirconium phosphate membranes provide power densities of 0.62 W/cm² at 100 °C.     

Forecast of Performance Parameters of Automotive Fuel Cell Systems – Delphi Study Results

Fuel cells are a promising propulsion technology option in sustainable and zero‐emission drivetrain strategies as they offer a high potential to significantly reduce well‐to‐wheel greenhouse gas emissions and the dependency on fossil energy resources. At the same time, the current technological performance of automotive fuel cell systems is not yet sufficient to meet market demands. Therefore, the technical development of fuel cells is a critical factor for a successful market introduction of fuel cell electric vehicles (FCEV). This paper describes the methodology and results of a two‐round Delphi Survey conducted by the Institut für Kraftfahrzeuge of RWTH Aachen University to assess the technological potential of polymer electrolyte membrane fuel cell (PEMFC) systems in automotive applications by 2030. The analysis of the current and future performance level of key performance indicators (KPI) of automotive fuel cell systems helps to identify critical performance parameters and to prioritize research and development demands. KPI analyzed in the Delphi Survey as forecast parameters include system efficiency, durability, power density, and specific power.     

Thermodynamics of Hydrogen Generation from Methane for Domestic Polymer Electrolyte Fuel Cell Systems

Low temperature fuel cells such as the Polymer Electrolyte Fuel Cell (PEFC) are preferably used for domestic applications because of their moderate operating conditions. Using the existing distribution system, natural gas is used as a source for a hydrogen rich gas to power this fuel cell type. The high requirements on the fuel gas quality as well as high conversion efficiencies for the small local gas processing units are critical aspects in the evaluation of decentralized fuel cell systems. In the present paper, three typical gas processing methods are evaluated for the supply of a hydrogen rich gas for PEFCs: steam reforming, partial oxidation, and autothermic conversion. All three processes are studied in detail by varying the relevant process parameters: temperature, pressure, steam to fuel ratio, and oxygen to fuel ratio. The results are graphically displayed in numerous nomograms. With the help of these graphs, regions of stable operation and the sensitivity to the operational parameters are discussed. For all three gas processing methods, the graphs generated display methane conversion, the hydrogen yield, and the yields of unwanted components, i.e., carbon monoxide and solid carbon. Although only steady‐state operating conditions were simulated, critical modes of operation, which might occur during start‐up or transient operation can easily be identified. For instance, operating conditions where soot is generated have to be avoided under all circumstances. All simulations were done with the Gibb's reactor model of a commercial simulation program. The Gibb's reactor model was found to be a suitable tool, since the simulated results compared well with reported literature data. According to the simulation results, the methane‐steam‐reforming process appears to be favorable for application to PEFCs. Methane conversion and hydrogen yields are highest for this process while the yield of CO is relatively low.     

A Membraneless Direct Borohydride Fuel Cell Using LaNiO3‐Catalysed Cathode

Direct borohydride fuel cell (DBFC) is one of the most exciting energy technologies that solve the hydrogen storage and safety issues by using aqueous solution of KBH₄ or NaBH₄. Here, we present a membraneless DBFC with perovskite‐type oxide LaNiO₃/C‐catalysed cathode. A significant finding from the electrochemical experiments is that it obviously shows that the existence of ions has almost no negative influence on the discharge performances of the LaNiO₃‐catalysed cathode. Therefore, the DBFC is designed without using an ion exchange membrane. The maximal power density of 127 mW cm^–2 is obtained at 65 °C under atmospheric pressure. A 500 h life test shows that the DBFC has good stability.     

Research of Flywheel System Energy Harvesting Technology for Fuel Cell Hybrid Vehicles

In this study, two fuel‐cell hybrid systems for the energy performance comparison of fuel‐cell hybrid vehicles (FCHVs) are presented. A Matlab/Simulink modelwas constructed, and the main power source was a fuel cell. A lithium battery and a flywheel battery were the auxiliary power sources. A vehicle driving test, FTP‐75 (Federal Test Procedure), was applied for four different control modes:mixed common output mode, normal driving charge mode, fuel‐cell mode, and braking mode. FTP‐75 simulated the energy requirements and energy output stateof the full‐motor hybrid system. The results show that the recovered energy of the flywheel battery was higher than that of the lithium battery, and the output power was close to the motor output curve. The flywheel battery can withstand rapid charging and discharging, which substantially reduces time and instantaneous motor current output. It can also effectively reduce the load on the motor. Finally, the flywheel battery enhanced the driving range of the hybrid vehicle to a greater degree than the lithium battery did under the same conditions. The overall energy consumption is reduced by 22.7%; corresponding to a hydrogen saving of 17.8 g.     

Model for the Degradation Performance of a Single‐Cell Direct Methanol Fuel Cell under Varying Operational Conditions

The effect of varying operating parameters on the degradation of a single‐cell direct methanol fuel cell (DMFC) with serpentine flow channels was investigated. Fuel cell internal temperature, methanol concentration, and air and methanol flow rates were varied in experimental tests and fuel cell performance was chronologically recorded. A DMFC semi‐empirical performance model was developed to predict the polarization curves of the DMFC and validated at different operating conditions. Performance degradation was observed and modeled over time by a linear regression model. Unlike previous studies, the cumulative exposure of the operating factors to the fuel cell was considered in the degradation analysis. The degradation model shows the cell voltage generation capacity does not significantly degrade. However, the Tafel slope of the cell changes with cumulative exposure to methanol concentration and air flow, and the ohmic resistance changes with cumulative exposure to temperature, methanol and air flow.     

Performance Analysis of a Stationary Fuel Cell Thermoelectric Cogeneration System

The main purpose of our study was to use an experimental method and system dynamic simulation technology to examine a proton exchange membrane fuel cell thermoelectric cogeneration system that provides both high‐quality electric power and heated water. In the second part of our study, we experimentally verified the development of key components of the fuel cell and conducted a comprehensive analysis of the subsystems, including the fuel cell module, hydrogen supply subsystem, air supply subsystem, humidifier subsystem, and heat recovery subsystem. Finally, we integrated all of the subsystems into a PEM fuel cell thermoelectric cogeneration system and performed efficiency tests and analysis of power generation, heat recovery, and thermoelectric cogeneration. After comparing this system's efficiency results using simulation and experimentation, we determined that the accuracy of the simulation values when compared to the experimental values was >95%, showing that this system's simulation nearly approached the efficiency of the actual experiment, including more than 53% for power generation efficiency, more than 39% for heat recovery efficiency, and more than 93% for thermoelectric cogeneration combined efficiency.     

Hydrogen Mass Transport in Fuel Cell Gas Diffusion Electrodes

An oxygen transport model derived for limiting current density operation was employed to explore its use for hydrogen transport. Limiting current data obtained from a variety of fuel cell designs (alkaline, proton exchange membrane, sulphuric acid) demonstrated the model's validity and allowed determination of the hydrogen mass transport coefficient, a key cell performance parameter. Under specific operating conditions, the proposed model is consistent with the continuous stirred tank reactor and the logarithmic mean concentration difference models. The proposed model is preferable because it is more general and derived from a specific physical mechanism. Experimental precautions needed to ensure well‐defined limiting currents without the presence of artefacts were reemphasized and expanded. Model use for predictive purposes is also briefly discussed.     

Comparative Study of PEM Fuel Cell Models for Integration in Propulsion Systems of Urban Public Transport

Steady state and dynamic simulations are performed in order to compare the models. Considering the external response of FC system integrated in the tramway hybrid system, both reduced models show similar results with an important reduction of computation time with respect to the complete model. However, the reduced model 1 shows better results than the reduced model 2 when representing the internal behaviour of FC system, so that this model is considered the most appropriate for propulsion system applications.     

Exergoeconomic Analysis of a Residential Hybrid PV‐Fuel Cell‐Battery System

A residential photovoltaic (PV)‐based hydrogen fuel cell (FC) system is analyzed using exergoeconomic methods, and its monthly performance is investigated. Mathematical models for predicting the power outputs of the PV and FC systems are presented. The results reported include the PV output and the shares attributable to the battery and the SOFC in supplying the electrical demand. Moreover, to study the performance of the hybrid system in supplying the daily demand, results are presented for two typical days in summer and winter. An exergoeconomic analysis is performed to determine the electricity unit cost over the system lifetime. The PV‐electrolyzer system is not able to produce a sufficient amount of hydrogen during winter days, so seasonal hydrogen storage is required to feed the FC. Power penetrations of the PV and the battery systems are at maxima during the summer months, while the penetration of the FC system reaches 67% in January and December. Due to its low efficiency (16%), the maximum exergy destruction occurs in the PV modules (86%). The unit cost of electricity varies on a monthly basis, reaching a minimum of 0.26 $ kWh^–1 in July and a maximum of 1.8 $ kWh^–1 in January and December.     

Performance Evaluation and Parametric Optimization of a Proton Exchange Membrane Fuel Cell/heat‐driven Heat Pump Hybrid System

With the help of the current models of proton exchange membrane (PEM) fuel cells and three‐heat‐source heat pumps, a generic model of a PEM fuel cell/heat‐driven heat pump hybrid system is established, so that the waste heat produced in the PEM fuel cell may be availably utilized. Based on the theory of electrochemistry and non‐equilibrium thermodynamics, expressions for the efficiency and power output of the PEM fuel cell, the coefficient of performance and rate of pumping heat of the heat‐driven heat pump, and the equivalent efficiency and power output of the hybrid system are derived. The curves of the equivalent efficiency and power output of the hybrid system varying with the electric current density and the equivalent power output versus efficiency curves are represented through numerical calculation. The general performance characteristics of the hybrid system are analyzed. The optimally operating regions of some important parameters of the hybrid system are determined. The influence of some main irreversible losses on the performance of the hybrid system is discussed in detail. The advantages of the hybrid system are revealed.     

Hydrogen Supplied ICEs and Fuel Cells for Commercial Vehicles

In view of the limited availability of fossil fuels and the necessity to reduce the output of emissions of greenhouse gases in the long term, the transport sector needs efficient, environmentally compatible drive solutions. Hydrogen, as a clean and sustainable fuel, offers a high implementation potential and can be used both in internal combustion engines and in fuel cells. In urban deployment the fuel cell drive has specific advantages and is suitable for use in city buses. Integration of high‐power energy storage systems improves fuel consumption and can reduce the costs of the drive system. In May 2000 MAN presented its first fuel cell bus, which was successfully deployed in passenger transport in various cities. The next FC‐bus, using hybrid fuel cell propulsion, is planned under the framework of the Bavarian hydrogen project at Munich Airport and will be tested from spring 2004 on. The first deployment of pre‐series bus fleets with fuel cells using hydrogen as fuel can be expected from the end of this decade onwards.     

Investigation of Ni Foam Effect for Direct Borohydride Fuel Cell

Ni foam has been used as a substrate for the anode electrocatalyst in our previous works. In this study, the effect of nickel foam as an anode electrode in direct borohydride cells has been investigated under steady state/steady‐flow and uniform state/uniform‐flow systems, since nickel has catalytic property. Cathode catalyst used has been 0.3 mg cm^–2 on PTFE‐treated Toray carbon paper. The results have showed that power densities have increased by increasing the temperature. Peak power densities of 5.01 and 9.55 mW cm^–2 have been achieved at 25 and 60 °C, respectively, for 1.5 mol dm^–3 NaBH₄. On the other hand, the electrochemical performance has not been significantly different by the sodium borohydride concentration; only a small increase of power density has been observed in steady state/steady‐flow system, and only a small decrease of fuel utilization ratio has been obtained in uniform state/uniform‐flow systems.     

Self Humidifying Hybrid Anion–Cation Membrane Fuel Cell Operated Under Dry Conditions

Hybrid fuel cells composed of a low‐pH proton conductive membrane in contact with a high‐pH anion conductive membrane were investigated. The effect of relative humidity (RH), ionomer content in the anion‐conductive electrode and the inlet gas flow rates were evaluated. The formation of water at the junction of the anion conductive member and proton conductive membrane is especially interesting because it can self‐humidify the fuel cell when dry gases are used. In situ alternative current (AC) impedance spectroscopy was used as a diagnostic tool to understand the performance limitations under different test conditions. The cell output increased at low RH compared to a traditional proton exchange membrane fuel cell. The cell current under dry conditions was limited by the availability of oxygen in the catalyst sites due to flooding in the electrode layer. The ionomer fraction of the high‐pH cathode plays a significant role in the cell performance. At high gas feed rates, water removal from the electrode layers increased and mitigated the effects of flooding. The hybrid cells were operated at steady‐state operation at 0.58 V and 200 mA cm^–2 using dry H₂/O₂ feeds at 80 °C.     

Operation of the Alkaline Direct Formate Fuel Cell in the Absence of Added Hydroxide

The direct formate fuel cell (DFFC) has recently been demonstrated as a viable alkaline direct liquid fuel cell (DLFC) that does not require addition of hydroxide to the fuel stream for operation. In this work, we report that the DFFC can produce significant power at low temperatures without added hydroxide, especially when compared with other alkaline DLFCs powered by alcohols. Using oxygen at the cathode, the DFFC powered by 1 M HCOOK achieves a maximum power density of 106 mW cm^–2 at 50 °C and 64 mW cm^–2 at 23 °C. Using air at the cathode, the same DFFC achieves a maximum power density of 76 mW cm^–2 at 50 °C and 27 mW cm^–2 at 23 °C. These power densities were achieved without addition of hydroxide to the fuel stream. Constant current operation demonstrates that the maximum power density can be maintained at least for several hours of operation. Finally, we use electrochemical analysis to demonstrate that the formate oxidation reaction is not dependent on pH between 9 and 14, which permits the use of formate fuel without added hydroxide in the DFFC. An alkaline DLFC that does not require added hydroxide is promising for safe and practical operation.     

Membrane Design for Direct Ethanol Fuel Cells: A Hybrid Proton‐Conducting Interpenetrating Polymer Network

A series of hybrid proton‐conducting membranes with an interpenetrating polymer network (IPN) structure was designed with the direct ethanol fuel cell (DEFC) application in mind. In these membranes, glutaraldehyde crosslinked poly(vinyl alcohol) (PVA) were interpenetrated with the copolymer of 2‐acrylamido‐2‐methyl‐propanesulphonic acid (AMPS) and 2‐hydroxyethyl methacrylate (HEMA) crosslinked by poly(ethylene glycol) dimethacrylate (PEGDMA). Silica from the in situ sol–gel hydrolysis of tetraethyl orthosilicate (TEOS) was uniformly dispersed in the polymer matrix. The membranes fabricated as such had ion exchange capacities of 0.84–1.43 meq g^–1 and proton conductivities of 0.02–0.11 S cm^–1. The membranes exhibited significantly lower fuel permeabilities than that of Nafion. In a manner totally unlike Nafion, fuel permeabilities were lower at higher fuel concentrations, and were lower in ethanol than methanol solutions. These behaviours are all relatable to the unique swelling characteristics of PVA (no swelling in ethanol, partial swelling in methanol and extensive swelling in water) and to the fuel blocking and swelling suppression properties of silica particles. The membranes are promising for DEFC applications since a high concentration of fuel may be used to reduce fuel crossover and to improve the anode kinetics for a resultant increase in both the energy and power densities of the fuel cell.